ABSTRACT Fetal alcohol spectrum disorder (FASD) is estimated to affect 3-5% of the population in the United States [1]. Prenatal alcohol exposure (AE) leads to significant perturbations of brain circuitry and persisting cognitive deficits [2, 3]. The cognitive impairments associated with FASD include abnormalities in executive functioning (EF) and working memory[4, 5]. These abnormalities stem from orchestrated structural changes in several key brain regions including medial prefrontal cortex (mPFC) and hippocampus (HPC). While HPC and mPFC have long been implicated in effective cognitive functioning, the critical role of the thalamic nucleus reuniens (RE), that controls infromation flow between these structures has only recently been appreciated. Our preliminary data have revealed that prenatal AE affects the structure of RE and leads to behavioral deficits in fronto-hippocampal functitoning. The proposed research will test an innovative and novel hypothesis that developmental AE disrupts the HPC-RE-mPFC circuitry by altering the integrity of the midline thalamic RE . In healthy animals RE is reciprocally connected with the HPC and the mPFC and has been shown to be critical for a variety of working memory tasks. It is noted that while mPFC does not send direct projections to HPC, it connects with HPC via RE. Our preliminary data using animal model of binge drinking during third trimester indicate that postnatal day (PD) 4-9 AE produces persistent structural damage and loss of cells in RE in adult rat that is expected to produce a disruption in the functional connections between the three regions: mPFC, HPC and RE. The proposed research will test the hypothesis thatbinge AE during third trimester produces neuronal loss in the RE and this leads to dendritic and synaptic reorganization in thalamic RE, which ultimately produces dysfunctional connectivity with prefrontal cortex and hippocampus. Further, we will determine whether binge AE targets this nucleus exclusively and specifically among the midline thalamic nuclei and whether it affects behavior that depends on integrity of HPC-RE-PFC circuitry.In Aim 1, we will use classic and state of the art viral tracing and phenotypic analysis to reveal the effect of postnatal binge AE on neuronal organization and connectivity of RE with mPFC and HPC. Furthermore, in Aim 2 we use a specific set of behavioral assays that will reveal whether loss of HPC-RE-mPFC connectivity is critical to behavioral maladaption observed in AE. Significance and Innovation: The proposed research is innovative because it will use current viral neural circuit mapping and will fill a critical gap in our understanding of the mechanisms through which fetal alcohol exposure influence HPC-RE-mPFC circuitry damage and cognitive impairment. Further, because executive functioning deficits are observed in children with FASD, these aims will elucidate the crucial role of HPC-RE-mPFC circuitry in constellation of behavioral deficits in FASD; thus this region may be a critical therapeutic target in the treatment of FASD.